1. Field of the Invention
The present invention relates to an ink jet recording apparatus that records on a recording medium by discharging ink, and also, relates to an ink jet recording head, and an ink jet recording method as well.
2. Related Background Art
A recording apparatus provided with the function of a printer, a copier, a facsimile, and the like, or a recording apparatus used as the output device for a complex type electronic equipment or work station including a computer, a word-processor, and the like, is structured to record images (including characters, symbols, and the like) on a recording medium (recording material) such as paper, cloth, plastic sheet, OHP sheet. A recording apparatus is classified into various types such as ink jet type, wire-dot type, thermal transfer type, and laser beam type, among some others, by the method that the recording apparatus adopts for recording.
In a serial type recording apparatus, which records while conducting the main scan in the direction intersecting with the conveying direction of a recording medium (sheet conveying direction or sub-scanning direction), a recording head serving as recording means, which is mounted on a carriage that travels (conducts main scan) along the recording medium, records images, and after the completion of recording of one-line portion, the sheet is fed for a designated amount (a pitch conveyance as a sub-scanning). Then, after that, images on the next line are recorded (main scanned) on the recording medium that has come to a stop again. Such operation is repeated to execute recording on the recording medium entirely. On the other hand, in a recording apparatus of full-line type that records only by the sub-scanning of a recording medium (recording material) in the conveying direction, the recording medium is set at a designated recording position, and after having executed recording on one-line portion altogether, a sheet feed of a designated amount (pitch conveyance) is conducted, and then, recording on the next line is executed altogether. Such operation is repeated to record on the recording medium entirely.
Of those types of recording apparatus, the ink jet type recording apparatus (ink jet recording apparatus) is the one that records by discharging ink from the ink jet recording head that serves as recording means to a recording medium, and for this type, recording means can be made compact with ease for recording images in high precision at high speed. This type of recording apparatus also has advantages, among some others, that recording is possible on an ordinary paper without giving any particular treatment thereto, and the running cost is made lower, and also, being non-impact type, it has a lesser amount of noises, while it makes easier to record color images using many kinds of ink (color ink, for instance). Also, there have been many demands on the materials of the recording medium (recording material) recordable by the ink jet recording apparatus. In recent years, developments have been made to meet such demands on the recordable materials. Thus, in recent years, in addition to the usual recording medium, such as paper (including thin paper and processed paper), and thin resin sheet (OHP and the like), the recording apparatus has been made capable of using cloth, leather, unwoven textile, and even metal and others as the recording medium therefor.
Particularly, for the ink jet recording apparatus, there have been strong demands in color recording and in high quality recording in recent years. To meet such demands, the apparatus is structured to be able to provide gradational representation by changing dot sizes for obtaining images in high quality. For example, there has been known the structure in which plural electrothermal converting elements (heat generating elements, or heaters) are provided in each inner part of the ink flow paths, which are communicated with the discharge ports of an ink jet recording head, respectively, and then, by the selective supply of electric signals to each of the electrothermal converting elements from a functional element circuit formed on a base plate, the amount of discharge ink per pixel (per discharge port) is changed to make the gradation recording of images possible. As a specific example of the structure of a recording head of the kind, it has been known that in one liquid path (ink flow path), plural electrothermal converting elements (heaters) are arranged in the discharge direction of ink (flow direction), and heaters to be driven or the number of heaters to be driven is selected so as to make the distance different between the discharge port and the heater to be driven in each liquid path (ink flow path), thus changing the discharge amounts of ink.
Also, as another structure, there has been known the one in which plural heaters each having different area are arranged in one liquid path (ink flow path), and by selecting heaters to be driven or the number of heaters to be driven in the same manner so as to change the discharge amounts of ink. Also, it has been generally practiced to execute the so-called pre-discharge, which does not participate in recording directly, in a designated location (at designated sequence) immediately before recording is started, for example, thus preventing defective discharge due to the presence of overly viscose ink in the vicinity of discharge port or in the ink flow path communicated with the discharge port or due to bubbles residing in the ink flow path. Further, as compared with a liquid droplet having large volume (large droplet), a liquid droplet having small volume (small liquid droplet) tends to be encountered with discharge defects immediately after recording is started. Therefore, as disclosed in the specifications of Japanese Patent Laid-Open Application No. 08-183186 and Japanese Patent Laid-Open Application No. 10-016222, when small liquid droplets are discharged for recording, the pre-discharge is executed with large liquid droplets (medium liquid droplets and large liquid droplets) having discharge amount larger than the discharge amount (by small droplets) at that time or to change the time intervals of pre-discharges in order to prevent discharge defects.
However, when a highly precise recording is performed at high speed for various images using an ink jet recording head of discharge amount modulating type in which plural heaters (electrothermal converting elements) are arranged in one ink flow path, there may be encountered some cases where technical problems should be solved as to the pre-discharge (which does not participate in recording directly) executable as one of processing operations in the discharge recovery process described earlier. For example, for recording only characters mainly in black ink, it is required to record thick at high speed, and also, for recording a photographic color images or the like, a highly precise recording is needed. Therefore, it is necessary to execute recording in black by use of large liquid droplets, and recording in colors by use of small liquid droplets. Also, for the small liquid droplets used for color recording, there has been tendency that the discharge amount of ink becomes increasingly smaller in recent years.
Also, it has been desired to highly densify the discharge ports of the recording head and the ink flow paths (liquid paths) communicated therewith for recording images in high precision, and the widthwise dimension of the discharge port is restricted significantly. In order to discharge large droplets in black with the discharge port the widthwise dimension of which is thus restricted, the size (surface area or the like) of the heater (electrothermal converting element) should be made larger or there is a method to make the opening sectional area of the discharge port larger. However, if the heater size is made too large, ink mist (sprayed ink) or the like is generated to invite the degradation of recording quality. Therefore, it is necessary to make the opening sectional area of the discharge port larger. To this end, the liquid path must be made higher than a certain height. On the other hand, when the small color droplets are discharged, the faster the discharge speed, the more precisely becomes the recorded images obtainable. Therefore, the size of the electrothermal converting element cannot be made too small. Under such circumstances, in order to discharge small color droplets, the size of the discharge port (opening sectional area) should be made smaller. Also, the smaller the discharge amount as in the case of small color droplets, the easier it becomes to cause discharge defects due to overly viscous ink in the vicinity of the discharge port or due to bubbles in the liquid path. Therefore, to eliminate such discharge defects, the pre-discharge is carried out by use of liquid droplets larger than the small droplets (medium liquid droplets or large liquid droplets). In this way, the overly viscous ink can be removed to a certain extent.
However, as described earlier, for the prevention of ink mist at the black discharge port, the sectional area of the discharge port is secured to discharge large liquid droplets. Also, the pre-discharges are conducted at the color discharge port with larger liquid droplets (medium liquid droplets or large liquid droplets) in order to eliminate discharge defects due to overly viscous ink or bubbles. As a result, the sectional configuration of the discharge port should be such that the height is larger in relation to the smaller sectional area. Thus, there is formed an excessive space between the discharge port portion on the incident side and the ceiling portion at the leading end of the liquid path, and then, even if the pre-discharge is conducted by use of medium liquid droplets or large liquid droplets, bubbles are not completely exhausted due to the existence of such excessive space, and bubbles remain in the excessive space eventually. Thus, there is a technical problem encountered that despite the execution of pre-discharge, defective recording may take place in some cases. Also, it is difficult to enable the aforesaid remaining bubbles to be completely exhausted by increasing the number of pres-discharges (shooting number of pre-discharges) using medium liquid droplets or large liquid droplets, and there is a probability that only a large amount of ink is wastefully consumed after all.
It is an object of the preset invention to provide an ink jet recording apparatus, an ink jet head, and an ink jet recording method, which make it possible to perform high-quality recording without causing recording defects, and also, without consuming ink wastefully by completely exhausting foams (bubbles) in the ink flow path by means of pre-discharge.
It is another object of the invention to provide an ink jet recording apparatus, an ink jet head, and an ink jet recording method, which make it possible to perform high-quality recording without causing recording defects, and also, without consuming ink wastefully by completely exhausting foams (bubbles) in the ink flow path by means of pre-discharge even when small liquid droplets are discharged with the ink flow path of the recording head having a large height but small area at the discharge port thereof, for example. It is still another object to provide an jet recording apparatus for recording on a recording medium by discharging ink form a recording head, in which at least two electrothermal converting elements each having different amount of heat generation, and driven each individually, are arranged in the ink flow path communicated with the discharge port of the recording head along the ink flow path each in different distance to the discharge port, and when the pre-discharge is performed without participating in recording, driving signals needed for discharging ink are supplied to the electrothermal converting element on the side near to the discharge port subsequent to being supplied to the electrothermal converting element on the side away from the discharge port.
It is a further object of the invention to provide an ink jet recording head for recording on a recording medium by discharging ink form discharge port, in which at least two electrothermal converting elements each having different amount of heat generation, and driven each individually, are arranged in the ink flow path communicated with the discharge port of the recording head along the ink flow path each in different distance to the discharge port, and when the pre-discharge is performed without participating in recording, driving signals needed for discharging ink are supplied to the electrothermal converting element on the side near to the discharge port subsequent to being supplied to the electrothermal converting element on the side away from the discharge port.
It is still a further object to provide an ink jet recording method for recording on a recording medium by discharging ink from a recording head, which comprises the steps of arranging at least two electrothermal converting elements each having different amount of heat generation, and driven each individually in the ink flow path communicated with the discharge port of the recording head along the ink flow path each in different distance to the discharge port, and supplying driving signals needed for discharging ink to the electrothermal converting element on the side near to the discharge port subsequent to being supplied to the electrothermal converting element on the side away from the discharge port when the pre-discharge is performed without participating in recording.
In accordance with the present invention thus described, foams (bubbles) in the ink flow path can be exhausted by means of the pre-discharge even when small liquid droplets are discharged with the ink flow path having large height but small area at the discharge port thereof, hence providing an ink jet recording apparatus, an ink jet recording head, and an ink jet recording method, which make it possible to perform high-quality recording without causing recording defects, and also, without consuming ink wastefully.